1. Field of the Invention
The present invention relates to a coil unit for a linear motor, more specifically relates to a technology for cooling the coil with the refrigerant.
2. Description of the Related Art
Conventionally, in exposing devices for manufacturing semiconductor devices and high precision machining devices, it has been required to position an object (for example, a wafer to be exposed or a workpiece) fast and precisely. As a device for precisely positioning used for that purpose, devices for converting a rotation of a rotary motion type motor into a linear motion through a ball screw, and linear motion type motors (so-called linear motors) are widely used.
Among them, the linear motor has a simple structure, includes a small number of parts, has merits that its linear motion is directly used, and positions an object fast. It also includes characteristics that its small friction resistance during driving increases the motion precision. Because of the reasons describes above, the linear motor has been becoming a mainstream as a linear drive device in all fields where a precise positioning is required, and is widely used in a manufacturing process for a liquid crystal display device, for example.
This linear motor generally comprises a magnetic pole unit provided with magnets, and a coil unit provided with a coil. Either one of the magnetic pole unit and the coil unit is connected with a certain base, and functions as a stator, and the other of them is connected with a moving table, for example, and functions as a movable element. The magnetic unit and the coil unit are separated by a certain gap to avoid a contact, and relatively move linearly while the gap is maintained.
A coil provided for the coil unit generates heat when an electric current is supplied. This generated heat transfers to the entire coil unit, and further to the base and the moving table, for example, connected with the coil unit. As a result, problems described below occur.
(1) The heat from the coil causes thermal expansions of the coil unit itself and an associated machine connected with the coil unit, and causes an error in a positioning precision. Specifically, when the associated machine connected with the coil unit is a low thermal expansion material (thermal expansion coefficient is 1xc3x9710xe2x88x926) of 100 mm in length, for example, a thermal deformation of 100 nm is generated when the temperature increases by 1xc2x0 C. If a positioning precision of the order of one nanometer is required, this thermal expansion prevents satisfying the requirement sufficiently.
(2) A laser interferometer or the like is installed in the vicinity of the linear motor to measure a motion of the linear motor. When the coil unit heats an atmosphere around to generate a xe2x80x9cfluctuationxe2x80x9d, a light path of laser light is influenced, and a measurement error occurs.
It is known as a technique for solving the problem in (1) that a refrigerant is flowed between a mounting surface to an associated machine, and the coil in the coil unit to prevent the heat transfer from the coil. However, this technique cannot restrain temperature of an atmosphere around the coil unit from increasing, and the problem in (2) still remains unsolved.
A coil unit shown in FIG. 13 and FIG. 14 is proposed to solve both of the problems in (1) and (2). The coil unit 10 is used for a linear motor 1, and is placed so as to oppose to magnets 3 in a magnet unit 2.
Specifically, this coil unit 10 is provided with a plate-shape coil 12 placed opposing to the magnets 3 while extended in a traveling direction X, and a shell 14 for storing the coil 12 inside, and passing a refrigerant through gaps 13 between itself and the coil 12 to cool the coil 12. On the other hand, the magnet unit 2 is provided with a base 4 whose cross section is in a U shape, and the magnets 3 installed on inner walls 4A opposing to each other in the base 4.
A mounting surface 16 agaist to an associated machine is formed outside of one edge in a widthwise direction Y of the shell 14, a supplying hole 18 is formed on one end in a lengthwise direction X of the mounting surface 16 for supplying the gaps 13 of the shell 14 with the refrigerant, and a draining hole 20 is formed on the other end for draining the refrigerant. When the coil unit 10 is connected with an associated machine on a xe2x80x9cfixed sidexe2x80x9d through this mounting surface 16, the coil unit 10 serves as a stator, and the magnet unit 2 serves as a movable element. Inversely, when the coil unit 10 is connected with an associated machine on a xe2x80x9ctraveling sidexe2x80x9d, the coil unit 10 serves as a movable element, and the magnet unit 2 serves as a stator.
The refrigerant supplied from the supplying hole 18 diffuses in the gaps 13 between the coil 12 and the shell 14, and exchanges heat with the coil 12. Thus, the coil 12 which generates heat due to a current is cooled, and the refrigerant is heated. Because the heated refrigerant is drained from the draining hole 20, the heat does not accumulate inside the coil unit 10, a radiation to the atmosphere around is reduced, and a transfer of the heat from the coil 12 to the mounting surface 16 is restrained, thereby reducing a thermal expansion of the associated machine. As a result, this linear motor 1 has a reduced influence on the outside caused by the heat generation from the coil 12, and provides a more precise positioning.
However, this coil unit 10 does not always provide a sufficient cooling effect. FIG. 15 specifically shows a schematic diffusion status of the refrigerant inside the shell 14. The refrigerant gradually spreads as A, B, C, . . . , becomes a parallel flow, converges as F. G. and H, and is finally drained from the draining hole 20. Because the refrigerant is heated as it moves toward the downstream side, the temperature increases roughly in this order of A, B, C, . . . E, G, and H.
As a result, especially, the temperature of the refrigerant close to the downstream side (E, G, and H) is much higher than that on the upstream side, the cooling efficiency decreases, and simultaneously the heat transfers to the shell 14 through the refrigerant in this high temperature state, and is radiated outside. Further, the heat transfers to the mounting surface 16 through the refrigerant in this high temperature state on the downstream side, and becomes a cause for inducing a thermal expansion of the associated machine.
This property unavoidably presents even if the pressure of the refrigerant (a supplying pressure) and the width of the gaps are designed relatively favorably. If the design is not favorable, it is highly probable that a part where the refrigerant hardly flows actually occurs, and the defect sometimes becomes more remarkable.
Because it is required to increase the flow rate of the refrigerant to increase the cooling efficiency for avoiding this problem, problems such as increasing the capacity of a recirculating pump for the refrigerant occur.
The present invention is devised in view of the problems describe above relating to the cooling.
A coil unit for a linear motor relating to the present invention comprises a shell for using a refrigerant to cool a coil of a linear motor, a main flow passage formed inside the shell while extending in a lengthwise direction of the coil for leading the refrigerant supplied from the outside into itself, and a plurality of branch flow passages, formed on the main flow passage at a predetermined interval in the lengthwise direction, for draining the refrigerant led into the main flow passage in a widthwise direction of the coil, where the refrigerant drained from the branch flow passages after flowing through the main flow passage, flows through a gap between the shell and the coil to cool the coil.
This coil unit leads and stores the refrigerant in the lengthwise direction of the coil, and simultaneously branches the stored refrigerant toward the widthwise direction. Specifically, the coil unit is structured such that the main flow passage leads the refrigerant in the lengthwise direction of the coil, then the refrigerant is drained from the plurality of branch flow passages while the pressure inside the main flow passage is increased approximately evenly in the lengthwise direction of the coil. As a result, the coil is cooled along the widthwise direction at the individual positions in the lengthwise direction, the coil is cooled more evenly than in the conventional structure where the refrigerant flows over the entire surface of the coil mainly in the lengthwise direction. Thus a local temperature increase can be prevented.
When the quantity of the refrigerant increases, it is only required to increase an anti-pressure capability of a periphery of the main flow passage, and the branch flow passages serve as an absorbing member to provide almost an equal pressure distribution across the lengthwise direction of the shell. As a result, a local high pressure on the upstream side as in the conventional structure is avoided, and it is possible to structure the shell while decreasing the thickness thereof, and to decrease the weight consequently.
It is preferable in the invention described above to provide the main flow passage extending in the lengthwise direction in the vicinity of one edge in the widthwise direction of the coil, and to form a second main flow passage extending in the lengthwise direction in the vicinity of the other edge in the widthwise direction of the coil for receiving the refrigerant having flown on the surface of the coil in the widthwise direction.
In this way, the refrigerant which has flown in the gaps between the coil and the shell (at a certain degree of high pressure) positively flows into the second main flow passage to release the pressure thereof. As a result, because a pressure gradient is formed in the widthwise direction from the main flow passage to the second main flow passage, the refrigerant flows evenly in the widthwise direction, and the entire coil is more evenly cooled. This constitution is especially suitable for cooling a coil relatively large in the widthwise direction.
It is preferable in the invention described above to form sub-flow passages in the lengthwise direction at downstream ends of the branch flow passages, for temporarily storing the refrigerant led out from the branch flow passages, and for draining the refrigerant on the surface of the coil.
In this way, the refrigerant which has flown from the main flow passage into the individual branch flow passages in a state with an equalized pressure flows into the sub-flow passages, and the pressure distribution of the refrigerant is diffused in the lengthwise direction again in these sub-flow passages. Thus, even if there remains a slight pressure deviation among the individual branch flow passages, it is possible to flow the refrigerant from the entire sub-flow passages in the widthwise direction at a pressure more evenly averaged over the entire length of the coil. Namely, these sub-flow passages serve as a buffer, and the refrigerant led out independently from the individual branch flow passages is further equalized.
It is preferable in the invention described above to provide the main flow passage extending in the lengthwise direction in the vicinity of one edge in the widthwise direction of the coil, to form a mounting surface for connecting the coil unit with an associated member on an outer peripheral surface of the shell on a side opposite to the coil through the main flow passage, and to use the main flow passage interposed between the mounting surface and the coil for restraining heat from the coil from transferring to the mounting surface.
This coil unit is connected with the associated member (including a moving member) whether the coil unit itself serves as a stator or a movable element. Because the main flow passage through which the refrigerant in the most cooled state (before cooling the coil) is interposed between the coil and the mounting surface, it is possible to efficiently restrain the heat from the coil from transferring to the mounting surface in the constitution described above. Further, because the direction of the heat transfer from the coil to the mounting surface is opposite to the direction of the refrigerant flowing to the coil surface through the main flow passage and the sub-flow passages, the heat from the coil hardly transfers toward the mounting surface. As a result, it is possible to reasonably combine the even cooling effect across the lengthwise direction of the coil, and the prevention of the heat transfer to the mounting surface.
It is preferable in the invention described above to set the predetermined interval in the lengthwise direction for forming the plurality of branch flow passages to become narrower from the upstream side to the downstream side of the refrigerant flowing through the main flow passage. This is based on the following idea.
The main flow passage actively leads the refrigerant in the cold state in the lengthwise direction of the coil, and the refrigerant in the cold state can cool even a part of the coil far from the supplying hole of the refrigerant in any one of the inventions described above. However, the pressure of the refrigerant supplied from the supplying hole to the main flow passage tends to decrease as it measures farther from the supplying hole, though it depends on a inflow resistance into the individual branch flow passages, and the flow rate may decrease (while the refrigerant is certainly cold). In this case with the constitution described above, because the interval for forming the branch flow passages becomes narrower from the upstream side to the downstream side of the refrigerant flowing through the main flow passage (namely, it becomes narrower as the location is separated farther from the supplying location of the refrigerant), the reduction of the flow rate on the downstream side is prevented, and an evener cooling effect can be obtained.
As a setting for the interval, it is possible to set such that the plurality of branch flow passages are grouped as a set, and the interval for the individual sets becomes narrower stepwise. Also there is a case where the branch flow passages cannot be provided evenly along the lengthwise direction because of a design reason, in this case, the plurality of branch flow passages may be formed on the main flow passage as a whole, setting the interval narrower from the upstream side to the downstream side. It is also preferable to set the interval wider more or less only in a vicinity at the downstream end in the lengthwise direction of the main flow passage while setting the interval narrower from the upstream side to the downstream side as a whole because a reaction force tends to increase the pressure in the vicinity at the downstream end.
As a similar idea, it is preferable to set such that at least either one of the width of the gaps between the coil and the shell, and the cross section area of the branch flow passages becomes larger from the upstream side to the downstream side of the refrigerant flowing through the main flow passage. Because this constitution increases the width of the gaps and the cross sectional area to compensate the decrease of the flow rate caused by the pressure loss on the downstream side, a more even cooling effect is provided.
When the second main flow passage in the lengthwise direction is formed in the vicinity of the other edge in the widthwise direction of the coil, it is preferable to further form a draining pipe in the widthwise direction including one end opened on an outer peripheral surface on a side of the main flow passage of the shell, and the other end for communicating with the second main flow passage where the refrigerant guided into the second main flow passage is drained through the draining pipe, and the refrigerant flows on the surface of the draining pipe from the main flow passage side to the second main flow passage side to restrain heat from the draining pipe from transferring to the shell.
Because the temperature of a refrigerant generally increases as it flows downstream in this type of a cooling structure using the refrigerant, the vicinity of the draining opening presents the highest temperature. Namely, the temperature of a vicinity of a part where a refrigerant after cooling is collected tends to become high, because the heat of the refrigerant is also collected there. In this case, because the refrigerant led by the main flow passage (in the cold state) directly covers the vicinity of the openings of the draining pipe in the constitution above, and simultaneously the refrigerant flowing in the widthwise direction around the draining pipes cools the draining pipe themselves, the heat from the draining pipe is prevented from transferring to the shell or the atmosphere around the shell, and an influence on the outside is kept to small even when the refrigerant at a high temperature is drained. Namely, even when the draining pipe provided in the widthwise direction drains the refrigerant at a high temperature, because the refrigerant flows around the draining pipe in the direction opposite to the draining direction, the refrigerant therearound keeps the heat influence on the outside small.
Also, because this structure supplies the refrigerant from the main flow passage side, and drains it from the same main flow passage side, it is easy to mount the coil unit on the associated machine, and to design a piping for the refrigerant.
As a variation of the present invention, it may adopt a coil unit for a linear motor which comprises a shell for using a refrigerant to cool a coil of a linear motor, the coil unit comprising an outer cover for storing the shell inside while maintaining a second predetermined gap, and for passing the refrigerant through the second gap for cooling the shell, a first outer main flow passage, formed in the vicinity of one edge in the widthwise direction of the shell inside the outer cover while extending in the lengthwise direction, for leading the refrigerant supplied from the outside into itself, and for draining the refrigerant to an outer surface of the shell in the widthwise direction, a second outer main flow passage, formed in the vicinity of the other edge in the widthwise direction of the shell inside the outer cover while extending in the lengthwise direction, for receiving the refrigerant having flown in the widthwise direction on the outer surface of the shell after flowing through the first outer main flow passage, and supplying the refrigerant into the shell, and a draining pipe for draining the refrigerant having flown on a surface of a coil inside the shell to the outside.
The coil unit relating to this constitution adopts a double cooling structure where the additional outer cover is provided around the shell. Further, the coil unit is structured such that the first outer main flow passage guides the refrigerant (in a low temperature state) in the lengthwise direction of the coil, and the refrigerant flows in the widthwise direction (from the one end to the other end) through the second gap between the shell and the outer cover after flowing through the first outer main flow passage. The refrigerant is supplied inside of the shell after flowing through the second outer main flow passage, then, flows on the coil surface in the widthwise direction (from the other end to the one end), and is drained from the draining pipe (in a state at the highest temperature).
The structure for cooling the coil surface and the outer surface of the shell using a so-called counter flow achieves an even cooling in the widthwise direction in addition to achieving an even cooling in the lengthwise direction, the temperature is equalized all over the coil unit, and the cooling efficiency increases much more than the conventional coil unit. As a result, a local temperature increase is prevented in the atmosphere around.
The refrigerant in the coldest state supplied inside the outer cover covers the refrigerant at the hottest state inside the shell just before being drained. Also, the refrigerant flowing inside the outer cover in a moderately cold state covers the refrigerant inside the shell in a moderately hot state (after cooling the coil) in the vicinity of the center in the widthwise direction. In this way, because the existence of the refrigerant inside the outer cover restrains the heat of the coil from transferring from the inside to the outside rationally, the temperature increase of the coil unit is reduced much more than the conventional coil unit.
Further, In the double cooling structure described above, an inner main flow passage may be formed on a side of the second outer main flow passage inside the shell while extending in the lengthwise direction, leads the refrigerant supplied from the second outer main flow passage into itself, and drains the refrigerant out on the surface of the coil inside the shell in the widthwise direction.
With this structure, when the flow of the refrigerant becomes uneven (disturbed) after the refrigerant has flown to the second outer main flow passage, because the inner main flow passage leads the refrigerant in the lengthwise direction again, and then leads out on the coil surface, the coil is cooled evenly.
A second inner main flow passage may be formed on a side of the first outer main flow passage inside the shell while extending in the lengthwise direction, receives the refrigerant having flown in the widthwise direction on the surface of the coil inside the shell, and drains the refrigerant from the draining pipe.
The refrigerant which has cooled the coil, and has become hot, should be drained outside as soon as possible, and the influence from the heat on the periphery should be restrained. With this structure, because the refrigerant in the high temperature state is promptly drained into the second inner main flow passage first, and does not stagnate in the periphery of the coil, a local high temperature state of the coil is prevented. Further, because the first outer main flow passage in the lengthwise direction into which the refrigerant in the coldest temperature state is led covers the second inner main flow passage in the lengthwise direction into which the refrigerant (in the hot state) is led, the heat transfer to the peripheral atmosphere and the machine mounting surface is restrained. As clearly stated above, the machine mounting surface for mounting this coil unit to an associated machine is provided on the outer periphery of the outer cover preferably on the side of the first outer main flow passage. This preference allows the first outer main flow passage to insulate the heat transfer from the coil.
In the invention described above, it is preferable to provide a supplying hole formed in the vicinity of one end in the lengthwise direction of the outer cover for supplying the first outer main flow passage with the refrigerant, a communicating hole formed in the vicinity of the other end in the lengthwise direction of the second outer main flow passage for supplying the refrigerant guided into itself into the shell, and the draining pipe for draining the refrigerant inside the shell at a position corresponding to a vicinity of the supplying hole inside the shell.
In this way, the refrigerant moves in a sequence of the supplying hole, the communicating hole, and the draining hole. It is a cooling structure where the refrigerant is supplied from the supplying hole, moves along diagonal lines of the coil unit, returns to a vicinity of the supplying hole again, and is drained from the draining pipe when viewed as a whole. Thus, an evener cooling effect is provided across the entire coil, and the temperature increase of the atmosphere around is restrained at an even higher level. Also, because the supplying side and the draining side are close to each other, the design for an outer piping becomes easy.
Further, it is preferable to provide the draining pipe so as to pass through a vicinity of the downstream side of the supplying hole in the first outer main flow passage. With this constitution, because the refrigerant flowing through the first outer main flow passage cools the outer peripheral surface of the draining pipe through which the refrigerant in the highest temperature state passes, the heat generated from the coil is recovered while a local temperature increase is restrained in the vicinity of the draining pipe on the coil unit, namely only the refrigerant inside the draining pipe is heated. The vicinity of the downstream side of the supplying hole approximately refers to a position inside the supplying hole in the lengthwise direction, and simultaneously close to the supplying hole.
As means for the first outer main flow passage for leading out the refrigerant in the widthwise direction on the outer surface of the shell, it is preferable to form a plurality of branch flow passages at a predetermined interval in the lengthwise direction on the first outer main flow passage, to use this the plurality of branch flow passages for individually branching the refrigerant led into the first outer main flow passage, and to lead out the refrigerant in the widthwise direction on the outer surface of the shell. There is no restriction on the number, the shape, the length, and the like of the branch flow passages, and any branch flow passages which can lead out the refrigerant in the widthwise direction can be essentially used.
Further, it is preferable to form sub-flow passages in the lengthwise direction at downstream ends of the branch flow passages for temporarily storing the refrigerant led out from the branch flow passages, and for leading out the refrigerant on the outer surface of the shell. With this structure, because the sub-flow passages diffuse the refrigerant led out from the individual branch flow passages in the lengthwise direction, and the refrigerant is led out on the outer surface of the shell while the pressure and the flow rate of the refrigerant are equalized in the lengthwise direction, the uniformity of the temperature distribution is increased on the outer peripheral surface of the coil unit. Because the branch flow passages or the sub-flow passages diffuses the pressure of the refrigerant in the lengthwise direction in the first main flow passage before the refrigerant flows in the widthwise direction, it is possible to decrease the thicknesses of the outer cover and the shell, and to constitute the coil unit relatively compact while the double cooling structure is adopted.
While the ideas describe above restrain the thermal influence from the coil unit on the atmosphere around and an associated machine as a major purpose, flowing the refrigerant in the opposite direction allows an application for increasing xe2x80x9cheat radiation capabilityxe2x80x9d of the coil unit.
Specifically, the coil unit used for a linear motor comprises a coil provided so as to oppose magnets of a linear motor, a shell for storing the coil inside while maintaining a predetermined gap, and for passing the refrigerant through the gaps for cooling the coil, an outer cover for storing the shell inside while maintaining second predetermined gaps, and for passing the refrigerant through the gaps for cooling the shell, a first guiding path, formed in the vicinity of one edge in the widthwise direction of the coil inside the shell while extending in the lengthwise direction, for leading the refrigerant supplied from the outside into itself, and for leading out the refrigerant in the widthwise direction on a surface of the coil, a second guiding path, formed in the vicinity of the other edge in the widthwise direction of the coil while extending in the lengthwise direction, for receiving the refrigerant having flown in the widthwise direction on the surface of the coil after the first guiding path, and for supplying the refrigerant into the second gap between the shell and the outer cover, and a draining hole for draining the refrigerant having flown on an outer surface of the shell to the outside.
Basically, this structure reverses the direction of the flow of the refrigerant (upstream/downstream) described above.
With this structure, because the refrigerant in the low temperature state cools the coil surface first, and then flows in the gap between the shell and the outer cover, the heat from the refrigerant is released outside. Because the coil is actively cooled, this structure suits especially to a case where it is required to restrain the temperature increase of the coil itself (rather than to restrain the temperature increase of the atmosphere around the coil unit) as much as possible in a high capacity linear motor. The entire description described above can inversely apply to the detailed structures.